Modern commercial buildings include an abundance of communications equipment. Individual offices within the building are often equipped with telephones and fax machines, as well as computers that are interconnected with other computers through high speed communication networks. For ease of administration, apparatus for interconnecting such equipment (with each other and with outside networks) is centralized via interconnection (cross-connect) panels that serve the entire building.
A typical cross-connect panel includes several 110-type connector blocks each having an array of insulation displacement contacts (IDCs) for terminating large bundles of telephone wires. IDCs are commercially available and designed to facilitate making mechanical and electrical connection to a wire--particularly a wire that is surrounded by dielectric insulation. Each IDC includes a pair of opposing contact fingers that strip insulation from a wire that is pressed between the contact fingers so that an electrical contact is made between the wire and the IDC. Each IDC accommodates a single wire pressed between its opposing contact fingers, and is so compact that many IDCs can fit into a small area.
Several arrays of IDCs may be used to terminate a bundle of wire from a telephone central office while other arrays on the cross-connect panel may be used to terminate bundles of wire from telephone equipment within the building. Interconnecting particular wires from one bundle with particular wires from another bundle is accomplished with a patch cord comprising a cord with a plug (patch plug) attached to each end. The cord includes several wires within a plastic jacket. The patch plugs include a number of contact blades that are designed to be pressed into an equal number of IDCs within an array thereof. Once wired, a patch plug is a multiple wire connector that may be installed and removed from the cross-connect panel for the purpose of branching off existing lines or connecting together discrete areas of the terminal field.
One type of patch plug used in connection with the 110-type connector block is described in U.S. Pat. No. 5,226,835, which is incorporated herein by reference. The patch plug includes a two-piece dielectric housing which snaps together and captures several conductors therein. Each of the conductors includes an insulation displacement contact at one end for receiving individual wires from a cord and a contact blade at the other end for inserting into the IDCs of the 110-type connector block. A cord comprising a bundle of insulated wires, surrounded by an insulating jacket, is prepared for connection to the conductors by stripping away a small portion of the jacket to expose the insulated wires. The insulated wires may then be placed into the underside of the upper housing member which includes narrow channels for holding the wires in fixed positions. Thereafter, the upper housing member may be snapped onto the lower housing member by pressing them together. The wires are then collectively pressed/seated into the IDCs of the conductors. A disadvantage of this type of patch plug is that the IDCs are exposed and may be damaged or bent either before or during assembly. In addition, because termination tools may damage the exposed contacts, termination is typically done by hand, which can result in inefficiencies and excessive waste.
Another type of patch plug is described in U.S. Pat. No. 5,460,545. This patch plug includes an insulative plastic housing having three separable parts, a lower first housing, an upper second housing and a contact insulator housing. The patch plug also includes a plurality of conductors in the insulator housing, each conductor having an IDC at one end and a blade portion at the other end. As with the previous patch plug, the IDCs of the conductors are exposed and subject to damage.
Both of the above mentioned patch plugs also present additional difficulties. First, since the patch plugs are limited in width size to permit installation of adjacent patch plugs to the 110-type connecting block without missing terminal locations that may require access, a very tight clearance exists between the endmost insulation displacement contacts of the conductors and the side walls of the patch plug housing, inhibiting the use of a contact protection block around the contacts. Second, since the wires remain in the housing, they must be carefully trimmed, adding to installation time and the increased possibility of error. Failure to adequately trim can result, among other things, in wires being jammed between the termination cap and the rest of the housing, preventing proper termination. Third, it is difficult to remove these patch plugs once they are mounted to a termination block, especially when several patch plugs are mounted side-by-side, since it is difficult to build up a sufficient grasping force on the upper and lower surfaces of the plug housing when attempting to pull the plug out.
An additional problem found in many patch plugs is the existence of crosstalk. This occurs when exposed wires or conductors carrying different signals are placed too close to one another, thereby allowing electrical interference between the signals. This often results in telephone users being able to hear other users' conversations, fax machine or computer signals, or static sounds. Generally, two conductors are required to complete a circuit and service each telephone line, fax machine or computer modem. The wires to complete each circuit are usually paired and inserted into the insulation displacement contacts in the patch plug adjacent to one another. This creates the situation where one conductor of one pair is connected to a different circuit than one adjacent conductor of an adjacent pair. Close proximity of electrical conductors of adjacent pairs is a major contributor of crosstalk. The conductors of a 110 patch plug must have specific spacing at the front of the patch plug in order to connect with an array of IDCs. These dimensions on prior art patch plugs are close enough to generate crosstalk between adjacent circuits.
Another disadvantage of the above mentioned patch plugs is that they do not provide for adequate strain relief for the cord comprising a bundle of insulated wires. Because arrays of IDCs in office settings are often installed in closets or other areas with limited floor space, it is common to mount these arrays on a wall. When a patch plug is used to connect wires to these wall mounted IDC arrays, the cord which is stripped and inserted into the back of the patch plug often hangs from the back of the patch plug. The patch plugs are composed of a hard plastic dielectric housing that terminate at their cord ends with an opening for inserting and securing the cord. When these patch plugs are used, the weight of the cord causes the hanging cord to bend at close to a ninety degree angle. The effect of this bending action is that the hard plastic opening in the patch plug housing tends to crimp the wires contained within the cord. This crimping can damage the wires, cause interference between the different signals carried in the wires, reduce the service life of the wires and cause a general degradation of the performance of the wires.
In view of the above, it should be appreciated that there is still a need for a patch plug that may be readily installed in the field by hand or by a punchdown tool, that may be readily removed and reinserted at a different location on the cross-connect panel having IDCs that are protected from damage, that minimizes crosstalk and other interference, and that provides adequate strain relief for the cords to which they are attached.